Coating



Patented ug. 7, '1934 ooATIivG Charles W. Gordon, Munster, Ind., assignor to The Superheater Company,` New York, N. Y.

Application November 6, 1931,sefia`1'N0. 573,369 2 Claims. (01;"137-75) i flvleans o'f prtecting superheater tubes or other articles subjected to furnace gases and the like have been proposed, lbut it has been difficult to y obtain ani-article having a protecting coating f which can be made without employing special processes or apparatus `and which is of reasonable cost.

It is the principal object `of the present invention to provide a composite article avoiding 10 fthe above mentioned difliculties.

The novel features of my invention are pointed out in the appended claims. The invention itself, together with its objects and advantages, will best be understood from a detail description herein- 1'15V below of several'articles selected from a number of possible embodiments of my inVentOlIl, Such description being given in connection with the accompanying drawing, in which Fig. 1 is an elevation of a portion of a coated S article, in accordance with my invention.

Fig. 2 is a vertical central section of the article shown in Fig. 1.

Fig. 3 is a transverse section of the article shown in Figs. 1 and 2.

25 Referring to the drawing more in detail, I have illustrated in Figs. 1 and 2 a superheater tube 10 of ferrous metal. Tubes of this character are often employed in superheating elements and for other uses which subject them 3'() to highly heated furnace gases of oxidizing character. Under the conditions of use in certain furnaces, articles of ordinary ferrous material deteriorate at a rate of speed prohibiting their commercial use. It is dimcult, also, to prevent rthe temperature of steam delivered by superheaters from rising above that desired when the flow and ring rates vary.

In accordance with my invention, the deterioration in furnaces of ferrous articles, such as superheater tube 10, is very greatly reduced, if

not eliminated, and variations in steam temperature reduced by surrounding the article with a layer or coating 12 of highly resistant material such as Fahrite, a high fusing diflicultly oxidizable alloy of iron and chromium, or of other metal of like non-oxidizing character. The coating 12 is in the form of a thinsheet which is Wrapped around the tube 10, the sheet 12 when Wrapped around the tube having its edges lying longitudinally of the tube on the side opposite thesource of heat and preferably substantially parallel to the axis thereof. However, I do not limit myself to this. The edges of the tube are secured when in place by weld metal, as shown at 14, so that the coating 12 is in good heat transferring relation to tube 10 along the line of` weld metal` 14. The coeiicient `of expansion of the ordinary steel tubing 10 being less than that of ther chrome steel coating 12, the coating l2 swells awayfrorn 'the tube 10 when heated and* creates thereby a space or loose contact at their interface between the two parts cutting down the transference of heat to the front face of the tube 10 and preventing it from being overheated. The coating l2, While subjected to high temperature is able to withstand it without undue deterioration, partly due to its inherent characteristics and partly to the heat radiated to the face of tube 12.

The edges of the coating 12 may be arranged in various ways within my invention. In the article illustrated in Figs. 1, 2 and 3, the edges of sheet l2 both lie liat against the surface of the tube -19, but are spaced apart slightly and beveled to vprpyide space for the V shaped body 14 of Weld metal which firmly units the edges of coating 12 to each other and also to the body of tube 10.

It will be noted that the arrangement shown, not only protects the metal of the ferrous base from the oxidizing furnace gases, but it also autor f matically reduces the maximum steam temperature and thereby helps protect the steam using' devices by reducing the flow of heat to the superheater tubes at times when there is danger that the steam temperature may rise too high.

It will be seen further that the arrangement of the article illustrated in Figs. 1, 2 and 3 has a maximum effect both in protecting the metal of the tube and in limiting the maximum steam temperatures from the fact that, the coating being fastened to the cooler face of the tube, almost the entire separation between the coating and the tube occurs on the hotter face of the article.

Since the thermal coeicient of expansion of layer 12 is not the same as that of tube 10, I provide means for accommodating the differing degrees of longitudinal expansion of tube 10 and layer 12 without straining the layers. In the arrangement shown for this purpose in Figs. 1 and 2, I provide an external bulge 2O in layer 12 which bends outwardly away from the outer surface of tube 10 giving an exterior pocket 21 within which 10 and 12 are not in contact. Bulge 20 extends entirely around the tube 10 and is made 105 suiciently large so that the metal of the bulge 20 may bend sufciently to accommodate anyV difference in expansion expected between parts 10 and 12 throughout a predetermined length of the article.' It will be understood, however, that 110' I do not limit myself to a bulge or corrugation formed as an integral part of the layer 12 for purposes of accommodating differential expansion of the parts, since I may use an overlapping joint or other means for this purpose.

When in use in a furnace, articles in accordance with my invention preferably are arranged so that the seam in the coating and the Weld metal 14 is at the rear or side of the article facing away from the furnace.

While I have illustrated only an oxidation resistant coating of the type having a longitudinal seam, it is clear that I may use seamless coatings. In this case also, the coating may be welded 'or otherwise secured to the tube. n

While all oxidation resistant materials now known have a higher thermal coecient of expansion than iron or steel, 'I do not limit myself to the use of such material, as the desired effect of having the coating expand away from the tube when heated will occur if the coating has a thermal coeicient of expansion equal to that of the tube because the thin coating heats up more rapidly and therefore expands more rapidly gjthan the tube when the fire is started in the furnace.

What I claim is:

1. An article of manufacture having a relatively oxidizable body and a layer of oxidation resistant metal in close contact therewith when cold but in non-adhering relation thereto and having its edges arranged to form a single longitudinally extending seam, and a weld joint for fastening the edges of said seam in iixed position and united to said body along a line on the face of the body which is to be the cooler side in use, said coating having a higher thermal coefficient of expansion than said body.

'2. An article of manufacture having a relatively oxidizable body and a layer of oxidation resistant metal enveloping said body and in contact therewith when cold but in non-adhering 'relation thereto throughout the larger part of the surfaces of said body and layer, and a heat conducting joint for fastening said layer to said body along a line on the face of such body which is to be the coolest side in use, said layer having a thermal coeiilcient of expansion not less than said body.

CHARLES W. GORDON. 

